Hi johnjunior, this sounds like a blocked cold feed to me[fairly common on older systems, had one last week]. You can prove this by draining some water out of the system[ boiler off] & watching for the ball valve to start filling in the loft[if it does it aint blocked]. Trouble is if it doesn't start filling, it's blocked & things will have just got worse! You can picture the problem, the blockage will need removing. Not many magic cures. Full drain down, trace pipe, usually blocked where it enters the system [ but could be anywhere]. Cut out pipework & unblock or replace. You'll be surprised how it can get so blocked. Still keen to have a go!!? Might be easier to get someone in. Good luck
Mark
Milk, no sugar ta.
Mark
Milk, no sugar ta.